1. Field of the Invention
The subject invention relates to display devices in general and to mathematical equation displays of a gas discharge type in particular.
2. Description of the Prior Art
Conventional gas discharge displays either were beset by spurious energization or "ghosting", or required special measures or equipment for an avoidance thereof.
In the case of mathematical equation displays, the problem was aggravated by the necessity of having to display arithmetic function signs. Because of these and similar problems, mathematical equation displays as found in arithmetic teaching machines and other equipment, were beset by design and utility limitations. In consequence, many prior-art apparatus limited themselves to the display of only two arithmetic function signs, typically a plus sign and a multiplication sign. Even then, these signs had to be displayed at different places, giving a jumpy character to the display and leading to confusion to the pupils.
A related drawback from this prior-art deficiency manifested itself in a necessity to present subtraction and division problems not in a normal manner, but rather in their inverse counterparts, thereby further adding to the pupils' confusion or to learning inefficiency.
This complex of problems was further aggravated by the fact that mixed displays of digits and mathematical signs necessitated the provision and energization of different segment electrode sizes, thereby entailing display brightness inequalities and rapid aging or display device deterioration.